1. Field of the Invention
The present invention generally relates to print control methods and tandem printing systems, and more particularly to a print control method for controlling a plurality of tandem-connected printers, and to a tandem printing system which is formed by the plurality of tandem-connected printers.
The tandem printing system is formed by a plurality of tandem-connected printers, and prints information on front and/or back sides of a continuous recording sheet. The tandem printing system is suited for making a large amount of prints at a high speed. By operating the plurality of tandem-connected printers in synchronism, it is possible to carry out a monochrome or color printing at a high speed. For example, by tandem connection of a printer which prints information on the front side of the continuous recording sheet and a printer which prints information on the back side of the continuous recording sheet, it is possible to carry out a duplex printing which prints on both the front and back sides of the continuous recording sheet at a high speed. In addition, by tandem connection of four printers exclusively for printing in yellow (Y), magenta (M), cyan (C) and black (K), it is possible to make color prints at a high speed.
2. Description of the Related Art
In the tandem printing system described above, it is extremely important to operate the plurality of tandem-connected printers in synchronism. If the printers do not operate in synchronism, a color error may be generated in the case of the color printing, and a page continuity may be lost by an error in the printed contents on the front and back sides in the case of the duplex printing. In addition, the continuous recording sheet may be damaged if a slack or margin of the continuous recording sheet between two adjacent printers is too large or too small.
A first example of the conventional tandem printing system is shown in FIG. 1 of a Japanese Laid-Open Patent Application No. 62-224821, FIG. 10 of a Japanese Laid-Open Patent Application No. 7-237336, and FIG. 3 of a Japanese Laid-Open Patent Application No. 11-231580. According to this first example of the tandem printing system, a host unit is connected to a controller of each of the printers, and the supply of print commands and print data to each of the printers and the management of operating states of each of the printers are carried out by the host unit. In addition, the controllers of each of the printers are connected via signal lines which exchange information necessary to operate the printers in synchronism with each other.
In addition, a second example of the conventional tandem printing system is shown in FIG. 2 of the Japanese Laid-Open Patent Application No. 11-231580. According to this second example of the tandem printing system, a host unit is connected to a master printer and slave printers, and the supply of print commands and print data to each of the printers and the management of operating states of each of the printers are carried out by the host unit. Moreover, controllers of each of the printers are connected via signal lines and a common print controller within the master printer, and information necessary to operate the printers in synchronism with each other is exchanged primarily under control of the master printer.
In the case of the tandem printing system shown in FIG. 1 of the Japanese Laid-Open Patent Application No. 62-224821, the information necessary to operate the printers in synchronism with each other is exchanged primarily under control of the controller of one printer, and this tandem printing system is similar to the second example of the tandem printing system in that one printer operates as the master printer.
In the first example of the tandem printing system, the controllers of each of the printers must be connected by signal lines, and the connection of the printers by the signal lines becomes complex as the number of printers increases. In addition, since the controllers of each of the printers are connected by the signal lines, the controllers of each of the printers must have a construction connectable to the signal lines. In other words, the printers must be designed exclusively for the tandem printing system, and the existing printers which are designed to be used independently cannot be used to form the tandem printing system. As a result, the cost of the tandem printing system becomes high. Moreover, the host unit must be aware of the system structure every time a user modifies the system structure, thereby increasing the load on the host unit which must also manage the operating states of each of the printers.
On the other hand, in the second example of the tandem printing system, the load on the host unit is slightly reduced by the provision of the common print controller within the master printer. However, it is still necessary to connect each of the printers by the signal lines. In addition, because the constructions of the master printer and the slave printer are different, in order to form the tandem printing system, it is necessary to use at least two kinds of printers designed exclusively for the tandem printing system. Consequently, the cost of the tandem printing system becomes high compared to that of the first example of the tandem printing system described above. In addition, every time the user modifies the system structure of the tandem printing system, it is necessary to clearly define the relationships of the master printer and each of the slave printers, and the host unit must accurately be aware of the system structure of the tandem printing system, thereby increasing the load on the host unit which must also manage the operating states of each of the printers.